1. According to the internet, a lightning strike contains about 5 billion joules or 5 GJ. How was this calculated?

  2. Another thing: Once the lightning strike a metal grounded rod, a current will flow. What type of that current and how much current? I think it will be a 325 MV current which is the voltage of the lightning. Is that correct?

    Edit: after i read a little bit about lightning , i found it was such a big scale , so how about a small electrostatic charge , say from a 1 MV van de graaff generator, i have a spark source ( my CRT TV :D ) and i will buy a multimeter and conduct some experiments , but i need to know what to expect

  • $\begingroup$ Related: physics.stackexchange.com/q/76251/2451 and links therein. $\endgroup$
    – Qmechanic
    Mar 23, 2014 at 17:44
  • 1
    $\begingroup$ You may be interested in reading more about electric currents, and how they differ from voltages. Note, in particular, that current is not measured in volts. Otherwise, +1. $\endgroup$ Mar 23, 2014 at 19:03
  • $\begingroup$ hahahaha :D , i know....what i meant was that the current has a voltage of 325 MV, 325 MV in the clouds and 0 V in the ground $\endgroup$
    – user28324
    Mar 23, 2014 at 21:13
  • $\begingroup$ Current doesn't have voltage just like speed doesn't have horsepower. They measure different things. Before a lightning strike, there is a huge voltage difference between the clouds and the ground. The presence of the voltage makes the current flow, but at the same time, the flow of the current makes the voltage go away. $\endgroup$ Dec 2, 2015 at 1:06

1 Answer 1


The energy in a static discharge is 1/2 * voltage * charge. For a 1MV VDG with a 1 meter sphere that's approximately 1/2 * 55µC * 1MV = 27.5J However that's too much to do experiments safely. You should stay far below 1J. Also mutimeters don't like sparks or high voltages of several kV.

  • $\begingroup$ 1- where did u get that equation? i understand the QV but why 1/2? 2- i dont think it will hurt the multimeter , once i let the spark through a wire where an LED was connected , it lit and didn't burn $\endgroup$
    – user28324
    Mar 23, 2014 at 22:57
  • $\begingroup$ The equation for the energy can by found here en.wikipedia.org/wiki/Capacitance. The article also tells you how to calculate the self capacitance of a sphere. Also sparks can hurt a multimeter and even if they don't you will not be able to measure the current or voltage. $\endgroup$
    – Tesseract
    Mar 24, 2014 at 5:24
  • $\begingroup$ i know an easier way thought i would share it with u , instead of calculating C and then use C=Q/V just use V=QK/r where K is coulomb constant and r is the radius. oh...u broke my heart :D , so i cant experiment , i kinda need some information about that current , any idea about where i can find it? $\endgroup$
    – user28324
    Mar 24, 2014 at 10:56
  • $\begingroup$ For accurate measurements you need a digital storage oscilloscope with a high voltage probe. However I'm not sure what exactly you want to measure. The peak current of the spark? $\endgroup$
    – Tesseract
    Mar 24, 2014 at 16:39
  • $\begingroup$ yes, no problem , i will just a year or so , joining engineering school , i can use their equipment then , cuz i cant afford these stuff $\endgroup$
    – user28324
    Mar 24, 2014 at 23:03

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